This proposal addresses the molecular control of neuronal cytoskeletal proteins by extracellular signals. The studies proposed here will focus on the regulation and function of the microtubule-associated protein MAP2, a multifunctional neuron-specific protein localized to dendrites. Previous studies under this project established that MAP2's phosphorylation state is regulated in situ by neural activity, especially via the neurotransmitter glutamate. Phosphorylation was shown to attenuate the binding of MAP2 to microtubules in vitro; however, effects on other MAP2 functions appear likely. The continuation of these studies is designed to advance our understanding of MAP2 function by performing detailed analyses of various MAP2 target interactions and their modulation by phosphorylation. Conditions for regulation of MAP2 phosphorylation via patterned synaptic activity will be examined in detail using rodent brain hippocampal slices. Phosphoepitope-specific antibodies will be used to examine the regulation of MAP2 in situ at defined sites, using slices or cultured neurons as model systems. The hypothesis that calcineurin plays an important role in MAP2 regulation will be tested using transgenic mice lacking the major neuronal isoform of calcineurin. Finally, the ability of MAP2 to interact with other molecules in vivo, including actin filaments and the cyclic-AMP dependent protein kinase, will be explored using fluorescence microscopy. These studies are relevant to several disorders in which abnormal development or maintenance of neural structure is manifest, including mental health diseases such as schizophrenia, neurodegenerative diseases such as Alzheimer's, and congenital disorders causing mental retardation.